36 Osbornite, meteoritic titanium nitride. By F. A. BANNISTER,M.A. Deputy Keeper, Mineral Department, British Museum. [Read January 23, 1941.] EVIL STORY-MASKELYNE described in 1870 the mineral con- Nstituents of the Bustee meteorite, which was observed to fall in 1852 near Bustee about 45 miles west of Goruckpur, India." The stone, weighing 1429 grams, now preserved in the British Museum collections, was found to consist chiefly of enstatite and diopside, and two con- stituents proved to be new minerals. Pale, chestnut-brown spherules of calcium sulphide, CaS, Story-Maskelyne named oldhamite'' and golden-yellow octahedra found embedded chiefly in the oldhamite he named osbornite. One side of the meteorite has been ground to reveal the nodules of oldhamite and a coloured lithograph in W. Flight's book 'A chapter in the history of meteorites' reproduces the appearance of the chief mineral constituents very well." The minute octahedra of osbornite are easily visible with a lens in the meteorite itself. Two chemical analyses of oldhamite, involving the solution of nearly a gram of that mineral in hydrochloric acid, left a residue of only 28 milligrams of the osbornite crystals, an amount too small in those days for a complete chemical analysis. Qualitative tests, however, seemed to have convinced Story-Maskelyne and Flight that osbornite contained calcium, sulphur, and titanium or zirconium, and they drew the rather odd conclusion that perhaps it was an oxysulphide of calcium, titanium, and/or zirconium. Story-Maskelyne was using the microscope for sepa- rating out the components of coarsely crushed meteorites, then a novel procedure, and sometimes yielding only very small samples of anyone constituent for subsequent study. The manipulation of a few tiny crystals and minute precipitates seventy years ago was no mean achieve- 1 N. Story-Maskelyne, Phil. Trans. Roy. Soc. London, 1870, vol. 160, p. 189; Proc. Roy. Soc. London, 1870, vol. 18, p. 146. 2 N. Story-Maskelyne, Rep. Brit. Assoc. Adv, Sci., 1863, for 1862 (32nd meeting, Cambridge), Trans. of Sections, p. 190. Preliminary note on the Bustee meteorite, with the first mention of the name oldhamite. 3 W. Flight, London, 1887, p. 118; reprinted from Geol. Mag. London, 1875, dec. 2, vol. 2, p. 408, plate facing p. 401. OSBORNITE, METEORITIC TITANIUM NITRIDE 37 ment and mistakes were bound to occur. Probably Story-Maskelyne was not at all satisfied with his results for osbornite, but fortunately he refrained from using further material so rare and limited in supply. Since then osbornite has not been reported from any other meteorite and there can be only a minute amount in the Bustee stone itself. In view of the difficulties which attended micro-chemical work in 1870 it would be unwise to show how the qualitative data published by Story-Maskelyne could have been differently interpreted. He did, however, publish two figures, the initial weight of osbornite analysed, viz. 28 milligrams and the weight 0·8 milligram of barium sulphate precipitated by barium chloride from the sublimate resulting from heating the crystals in a stream of chlorine. These figures correspond to only 4 °10 of sulphur so that sulphur can scarcely be one of the chief elements present. The same remark applies to calcium whether com- bined as sulphide or oxysulphide. Story-Maskelyne had no difficulty in establishing the true symmetry of osbornite. He measured the interfacial angles of several crystals and found them all to be regular octahedra. It seemed to me probable that if the symmetry were cubic then an X-ray photograph might give additional information, perhaps a simple clue to the chemistry of the mineral. A crystal measuring 1/10 mm. across was picked out from one of the oldhamite spherules and rotated about an octahedral edge. The patterns obtained from this and another crystal rotated about a [111] axis revealed that osbornite has a cubic face-centred lattice with cell-edge 4·235A. On consulting tabulated cell-edges of cubic sub- stances! it seemed likely that artificial titanium 'cyanonitride' with rock-salt structure and cell-edge 4·24A. should yield the same type of X-ray photograph as osbornite. This was readily confirmed by photo- graphing several specimens of so-called titanium' cyanonitride' in the British Museum collections. This compound is found in slags and bears from blast furnaces either singly or in groups of sharp copper-coloured cubes up to several millimetres across in a matrix of green slag often with abundant graphite. Both osbornite and the titanium' cyanoni- tride' have a metallic lustre and excepting the darker colour of the latter certainly show a marked resemblance as well as yielding closely similar X-ray patterns. Flight2, himself knew of the existence and ap- pearance of titanium' cyanonitride' and it was unfortunate that his 1 T. E. Knaggs and B. Karlik, Tables of cubic crystal structure of elements and compounds. London, 1932, p. 30. [~I.A. 5-171.J 2 Footnote on p. 120 of his book, but not in Geol. Mag. (loc. cit.). 38 F. A. BANNISTER ON own qualitative tests suggested zirconium rather than titanium as a constituent of osbornite. Entirely satisfactory confirmation of the presence of titanium in osbornite was obtained by further X-ray and qualitative chemical tests. Titanium' cyanonitride' is known to change to titanium dioxide when heated in air.! A crystal fragment of titanium' cyanonitride' was first heated to about 8500 C. The sharp cube edges and corners were found to be rounded after this treatment. Under the microscope the original cube faces were seen to be polycrystalline and the X-ray photograph showed that the compound had altered to oriented rutile. A crystal of osbornite was subjected to the same treatment. The tiny octahedron also lost its sharp edges and developed polycrystalline sur- faces. Moreover, the metallic lustre and golden colour were replaced by a translucent pale yellow appearance. This altered crystal yielded a rutile pattern and when crushed in methylene iodide gave birefringent fragments with no trace of any other component. The specific gravity of the rutile pseudomorph is 4,10, very close to the lowest values for rutile, 4·123, given in L. J. Spencer's tables." The X-ray pattern, specific gravity, and microscopic tests of the rutile pseudomorph after osbornite show that titanium is the chief metal present in the original mineral. Dr. M. H. Hey produced some equally convincing colour re- actions for titanium from four crystals of osbornite and has further shown that neither calcium nor sulphur can be detected. It is not un- likely that both these elements found by Flight were due to contamina- tion of the osbornite with a very small amount of oldhamite. Since there is insufficient osbornite available for a complete chemical analysis, Dr. Hey hopes later to make an approximate micro-chemical analysis. In the absence of a direct determination of nitrogen and carbon the cell-edge measurement and colour identify osbornite almost certainly with titanium nitride. The identification depends upon a considerable amount of previous work which has been carried out upon titanium' cyanonitride' and the two end-members of the series titanium nitride-titanium carbide, to which it belongs. W. H. Wollaston," in 1823, published some interesting data on crystals from the slag of iron works at Merthyr Tydfil. He described them as cubes like pyrite with the lustre of burnished copper, specific gravity 5,3, which scratched quartz and possessed a high electrical conductivity. 1 F. Wohler, Annalen der Chemie und Pharmacie, 1850, vol. 73, p. 34. 2 L. J. Spencer, Min. l\'lag., 1927, vol. 21, pp. 356 and 364. 3 W. H. \Vollaston, Phil. Trans. Roy. Soc. London, 1823, p. 17. OSBORNITE, METEORITIC TITANIUM NITRIDE 39 He was probably the first to recognize the metallic-like properties of the substance and for that reason he wrongly identified it as metallic titanium. F. Wohler (1850, loco cit.) first analysed similar material from a blast furnace in the Harz Mountains, and found that intimate intergrowth with graphite made complete separation from the latter difficult. His analysis in table I gives the content of carbon in titanium ,cyanonitride' as 3·64 % and he is responsible for the formula TisCN4 generally found in the literature. E. A. Rudge and F. Arnall! separated similar material from slag from a blast furnace converting Spanish haematite ore to pig-iron. They took especial care to free the titanium 'cyanonitride' from graphite by powdering finely in an agate mortar, passing through a 120-mesh sieve, then treatment with HCI to remove iron and HF to remove Si02, after which the bulk of the graphite was removed by flotation in a heavy liquid of specific gravity 3. In this way they found that the carbon content was up to 1 % (see table I), whereas clean crystals of the 'cyanonitride' visibly free of graphite gave carbon contents up to 3·4 0/0. v. M. Goldschmidt? published the first X-ray measurements on titanium' cyanonitride' (Wohler's material) and showed that the substance possesses the rock-salt type of crystal- structure. This material gave the cell-edge dimension 4·243A. Four specimens of titanium 'cyanonitride' from various blast-furnace slags now preserved in the British Museum collections have been X-rayed with a view to determining whether there is any appreciable variation in cell-edge dimensions. Three of the four specimens have a cell edge 4·24...t. and one gave 4·23A. Since the error due to film shrinkage, &c. is approximately ±O·OlA, within these limits it can be said that speci mens of titanium' cyanonitride' from different slags have the same unit-cell dimensions. Specimens of artificial titanium nitride and titanium carbide have also been photographed and give cell-edge values close to those reported by previous workers (tables II and III).